Intermittent control with a normally open thermal switch for windshield wiper system

ABSTRACT

An intermittent control for a windshield wiper system. One of the two motor terminals is connected to a battery and the second motor terminal is connected to ground through the conventional park switch. In parallel with the park switch is a bimetal element whose contacts are normally open and are closed as a resistance element heats up. The resistance element is connected in series with a potentiometer between the battery and ground. During each wipe cycle, no current flows through the resistance element and potentiometer, the resistance element cools and the bimetal element contacts open. During each dwell period, current flows through the resistance element and the potentiometer to heat the bimetal element. The dwell period is determined by the setting of the potentiometer. It is also possible to automatically vary the dwell period by including a thermistor in series with the resistance element, the thermistor being heated by an additional resistance element connected in the motor circuit. The drier the windshield, the greater the motor current and the higher the temperature of the additional resistance element. The impedance of the thermistor increases with the temperature of the additional resistance element to increase the dwell period.

United States Patent 12 Claims, 2 Drawlng Figs.

[52] U.S.Cl 318/443, 318/472 [51] lnt.Cl 860s 1/08 [50] FieldotSeareh318/443 WW, 47l, 472, 473; l5/250.02, 250.l2

[56] References Cited UNITED STATES PATENTS 3,148.399 9/1964 Zieglerl5/250.02 3,487,492 l/l970 Bischoff 3I8/443X 40 I4 Z E Inventors WillisE. Rieman Skaneateles; John J. Beck, Seneca Falls; Edward R. Betz,Auburn, all of N.Y. Appl. No. 879,236 Filed Nov. 24, 1969 Patented Nov.30, 1971 Assignee Gull & Western Systems Company New York, N Y.

INTERMI'I'TENT CONTROL WITH A NORMALLY OPEN THERMAL SWITCH FORWINDSHIELD WIPER SYSTEM Assistant Examiner-Robert J. HickeyAuorney-Amster & Rothstein ABSTRACT: An intermittent control for awindshield wiper system. One of the two motor terminals is connected toa battery and the second motor terminal is connected to ground throughthe conventional park switch. In parallel with the park switch is abimetal element whose contacts are normally open and are closed as aresistance element heats up. The resistance element is connected inseries with a potentiometer between the battery and ground. During eachwipe cycle, no current flows through the resistance element andpotentiometer, the resistance element cools and the bimetal elementcontacts open. During each dwell period, current flows through theresistance element and the potentiometer to heat the bimetal element.The dwell period is determined by the setting of the potentiometer. Itis also possible to automatically vary the dwell period by including athermistor in series with the resistance element, the thermistor beingheated by an additional resistance element connected in the motorcircuit. The drier the windshield, the greater the motor current and thehigher the temperature of the additional resistance element. Theimpedance of the thermistor increases with the temperature of theadditional resistance element to increase the dwell period,

INTERMI'ITENT CONTROL WITH A NORMALLY OPEN THERMAL SWITCH FOR WINDSHIELDWIPER SYSTEM This invention relates to windshield wiper systems, andmore particularly to arrangements for controlling the intermittentoperations thereof.

Conventional windshield wiper systems, powered by DC electric motors,cycle continuously at a selected speed until manually switched off.However, there are a number of systems in the prior art which allow thedriver to switch from a continuous operation to an intermittentoperation in which a dwell period follows each wipe cycle. A dwellperiod between wipe cycles is advantageous at times when the windshieldis only partially wet and the demand for wiping is less than the normallow speed operation. But the prior art intermittent wiper controlsystems are generally complicated, expensive, and tend to have poorcontrol characteristics.

Some of the prior art systems also provide for an automatic variation ofthe dwell period-the dwell period increases as the windshield becomesdrier. These automatic control systems suffer from the samedisadvantages as the manually controlled intermittent dwell systems.

' It is a general object of our invention to provide manual andautomatic intermittent wiper control systems which are simpler, morereliable, and cheaper than those of the prior art.

Briefly, in accordance with the principles of our invention, a bimetalelement is provided for controlling the turning on of the wiper motor.Following any wipe cycle, the bimetal element is in a cooled conditionand its contacts are open. Current flows through a heating elementassociated with the bimetal element and as the element heats up itscontacts come closer together. When the contacts engage each other themotor is turned on; the motor then completes its cycle without requiringa connection through the contacts of the bimetal element, and thebimetal element cools in preparation for another heating cycle followingthe end of the wipe cycle.

The length of the dwell period is detennined by the time required forthe bimetal element to heat sufficiently to the point where the contactsclose. In the manual system, the heating element for the bimetal elementis in series with a potentiometer. The magnitude of the current throughthe heating element, that is, the time required for the contacts toclose, is dependent upon the setting of the potentiometer. In theautomatic control system, in addition to the potentiometer (which stillallows some manual control) the heating element is placed in series witha thermistor. The impedance of the thermistor is determined by thetemperature of a resistance element placed in series with the motorwinding. The greater the drag on the wiper blades, the greater the motorcurrent and the hotter the resistance element. This in turn increasesthe thermistor impedance to cause a longer dwell period. Consequently,the dwell period increases as the windshield becomes drier (a drywindshield produces the greatest drag). A second thermistor, alsocontrolled by the temperature of the resistance element, can be placedin series with the motor winding to control the motor speed-the drierthe windshield, the slower the motor.

It is a feature of our invention to provide a bimetal element in acircuit for initiating the operation of a windshield wiper motor, thebimetal element determining the dwell period between wiping cycles.

It is another feature of our invention to control the current forheating the bimetal element by varying an impedance, the impedance beingvaried either by manual operation of a potentiometer or by a thermistorheated by a resistance element connected in the motor circuit.

Further objects, features and advantages of our invention will becomeapparent upon consideration of the following detailed description inconjunction with the drawing, in which:

FIG. 1 depicts a first (manual) illustrative embodiment of ourinvention; and

FIG. 2 depicts a second (automatic) illustrative embodiment of ourinvention.

FIG. 1 depicts a conventional DC motor 11 used in a windshield wipersystem. Although not shown in the drawing, it is to be understood thatthe system is provided with a crank arm connected to the output shaft ofthe motor for powering the windshield wiper linkage. Also, while thesystem of FIG. I is a constant-speed system, it will be apparent tothose skilled in the art that the invention is applicable tomultiple-speed motors. The invention is applicable to such motors withpermanent magnet or wound fields, and to motors with and withoutdepressed park capabilities.

Cam 12 rotates with the output shaft and controls the position of camfollower 37. As the cam follower moves, so does linkage 13. Contactelement 14 follows linkage 13 as shown symbolically by dotted line 40.Cam 12 is so arranged that contact 14 engages contact 31 when the wiperblades are in the bottom portion, or park position, of the wipe cycle.Contact element 14 is the conventional park switch of a windshield wipermotor. During the wipe cycle, contact 14 is grounded through contact 30.

For normal, continuous cycling, switch l8ais moved from ofi (0) positionto the normal (N) position. Ground is extended through the switch toconductor 36 connected to one end of the motor circuit. The other end isconnected to potential source 32. The system continues to cycle untilswitch l8ais moved to off (0) position. The motor does not stopimmediately because an alternate ground path is provided throughcontacts 14 and 30. Instead, the motor continues to complete the wipecycle in progress until contact 14 switches from contact 30 to contact31 and the ground path is broken.

Switch 18bis ganged with switch 180. When the two switches are in thenormal (N) positions, switch l8bhas no effect on the system operation.As soon as the switches are turned off, however, switch l8bis connectedto the respective off (0) terminal, contact 31 is extended throughswitch l8band resistor 33 to one end of the motor circuit. Initially,this has no effect on the system operation because contacts 31 and 14are not in engagement. However, at the end of the wipe cycle inprogress, contact 14 connects contact 31 to the other end of the motorcircuit. At this time resistor 33 is placed across the motor winding.The resistor is only a few ohms in magnitude; the motor winding currentflows through the resistor and quickly dissipates. As is known in theart, resistor 33 serves as a brake to cause the motor to come to anabrupt halt.

When it is desired to operate the system in the intermittent mode,switch l8ais moved to the intermittent (I) position. It is desirable tohave the wipers come on immediately. Were switch 18ato be moved-directlyto'the intermittent (l) position, a dwell period would precede the firstwipe cycle. In order to have the wiper motor turn on immediately, switchl8apasses over momentary contact segment 35 as it is moved from the off(0) position to the intermittent (I) position. Ground is extendedthrough switch l8aand the contact segment to conductor 36, connected toone end of the motor circuit. The motor turns on and as soon as camfollower 37 has been forced out of the cam depression, contact 14engages contact 30 and an alternate ground path is provided for themotor. The time required to move switch l8apast contact segment 35 issufiicient to allow contact 14 to be switched from contact 31 to contact30.

With switch 18a in the intermittent (I) position, ground is applied topotentiometer tap 38. With contact 14 connected to contact 30, conductor36 is also at ground potential. Consequently, no current flows fromconductor 36 through resistance element 16 and potentiometer 17 becausethere is no voltage drop across the series circuit. However, as soon asthe motor turns off at the end of the wipe cycle, contact 14 no longerengages contact 30 and conductor 36 is no longer grounded. Instead,conductor 36 is connected through two alternate paths to battery 32. Onepath is through the motor winding and the other is through contacts 14and 31, switch l8band resistor 33. The latter path ofiers minimalresistance and consequently the potential of conductor 36 is essentiallythat of battery 32. Current flows through resistance element l6,potentiometer 17, tap 38 and switch 18am ground. As the current flowsand the resistance element heats up, the bimetal element moves andcontact 34 comes closer to contact 15. Eventually, when the two contactsengage each other, ground potential is extended through switch lfilaandthe two contacts to conductor 36. The ground potential on conductor 36once again starts the motor operation, the motor thereafter being heldon by engagement of contacts l4 and 30.

With conductor 36 grounded once again, current no longer flows throughresistance element 16, the bimetal element cools, and contacts and 34open as shown in the drawing. (It should be noted that, as shown in thedrawing, contact 34 serves as the bimetal element itself and the contactfor conducting the motor current at the start of each cycle. As is knownin the art, two separate elements may be provided for this purpose-oneserving as the contact element and the other being the bimetal elementfor moving the contact element as it heats up.)

The dwell period is determined by the time required for the bimetalelement to heat sufficiently to close the contacts. This is in turndetermined by the setting of potentiometer tap 38. The lower thepotentiometer setting, the greater the impedance and the less thecurrent through the resistance element. The less the current through theresistance element, the greater the dwell period.

Switch 18bwhen the intermittent 1) position, connects contact 31 toresistor 33. Resistor 33 serves as a brake resistor following each wipecycle to bring the motor to an abrupt halt. The brake resistor functionsin the same manner both during the intermittent operation and at the endof the last wipe cycle in progress when the system is turned off. It isonly when the system is operated in the normal mode, where there is nodwell period, that brake resistor 33 is not connected across the motorwinding to brake the motor at the end of each wipe cycle.

The system of FIG. 2 is the same as that of FIG. 1, except for thefollowing differences:

a. Resistance element 19 and thermistor 21 are connected in seriesbetween battery 32 and the motor winding, and

b. Potentiometer tap 38, instead of being connected directly to theintermittent (1) terminal position for switch 18a, is connected to thisterminal position through thermistor 20.

Both thermistors 20 and 2] present impedances which are determined bythe temperature of resistance coil 19, the resistance element beingheat-coupled to both thermistors, The resistance element is in serieswith the motor winding. Since its temperature is proportional to themotor current, and the motor current is in turn a function of the dragon the wiper blades, the temperature of the resistance element is ameasure of the dryness of the windshield-the drier the windshield, thehotter the resistance element, Thermistor 20 increase impedance as thetemperature of resistance element 19 increases. Since thermistor 20 isin series with potentiometer tap 38, it is apparent that the dwellperiod is determined not only by the setting of the potentiometer tap,but also the impedance of the thermistor. As the windshield becomesdrier, the temperature to resistance coil 19 increases and the impedanceof thermistor 20 increases. This in turn results in a longer dwellperiod which is the desired eiTect; as the windshield becomes drier thefrequency of the wiping cycles can' be reduced.

It is also desirable to have the motor slow up as the windshield becomesdrier since the greatest wiper speed is necessary only when thewindshield is wet. As the windshield becomes drier and the temperatureof resistance coil 19 increases, the impedance of thermistor 21similarly increases. Since the thermistor is in series with the motorcircuit, a reduced current flows as the impedance of thermistor goes up.This in turn results in a slower motor speed.

Although the invention has been described with reference to particularembodiments, it is to be understood that these embodiments are merelyillustrative of the application of the principles of the invention Forexample, instead of providing potentiometer 127 to vary the dwellperiod, the heating current can be held constant and the relativepositions of bimetal contact 34 and mating contact 15 can be adjusted.Thus, numerous modifications may be made in the illustrative embodimentsof the invention and other arrangements may be devised without departingfrom the spirit and scope of the invention.

What is claimed is:

l. An intermittent control for windshield wiper system comprising amotor for driving windshield wiper blades through a wipe cycle, saidmotor including two terminals, first means for connecting a first one ofsaid two terminals to a source of a first potential, and second meansfor connecting the second one of said two terminals to a source of asecond potential, said second connecting means including two parallelpaths, a first of said paths including a motor park switch and a secondof said paths including a bimetal element and a heater resistanceelement therefor, said bimetal element having normally open contacts andoperative to close following a dwell period after each wipe cycle, theopening of said normally open contacts being dependent on the coolingrate of said bimetal element.

2. An intermittent control for a windshield wiper system in accordancewith claim 1 further including manually adjustable means for varying theclosure time of said bimetal element.

3. An intermittent control for a windshield wiper system in accordancewith claim 2 further including an additional resistance elementconnected in series with said motor terminals, and a thermistorheat-coupled to said additional resistance element and connected inseries with said resistance element.

4. An intermittent control for a windshield wiper system in accordancewith claim 3 wherein said manually adjustable means is a variableresistance connected in series with said heater resistance element.

5. An intermittent control for a windshield wiper system in accordancewith claim 3 further including an additional thermistor heat-coupled tosaid additional resistance and element connected in series with saidmotor terminals for controlling the speed of said motor in accordancewith the temperature of said additional resistance element.

6. An intermittent control for a windshield wiper system in accordancewith claim 2 wherein said manually adjustable means is a variableresistance connected in series with said heater resistance element.

7. An intermittent control for a windshield wiper system in accordancewith claim 3 further including an additional resistance elementconnected in series with said motor terminals, and a thermistorheat-coupled to said additional resistance element and connected inseries with said heater resistance element.

8. An intermittent control for a windshield wiper system in accordancewith claim 7 wherein said motor park switch is operative to connect saidsecond motor terminal to said source of said second potential when saidmotor is out of its park position and further including a brakeresistance, said motor park switch being further operative to connectsaid brake resistance across said switch tenninals when said motor is inits park position.

9, An intermittent control for a windshield wiper system in accordancewith claim 1 further including switch means having three positions, afirst of said positions for deenergizing said motor, the second of saidpositions for connecting said second motor terminal to said source ofsaid second potential bypassing said second connecting means, and thethird of said positions for enabling the operation of said second pathconnecting means.

10. An intermittent control for a windshield wiper system in accordancewith claim 9 further including means operative when said switch means ismoved from said first position to said third position for momentarilyproviding an alternate path from said second motor terminal to saidsource of said second potential.

12. An intermittent control for a windshield wiper system in accordancewith claim 11 further including means operative when said switch meansis moved from said first position to said third position for momentarilyproviding an alternate path from said second motor terminal to saidsource of said second potential.

1. An intermittent control for windshield wiper system comprising a motor for driving windshield wiper blades through a wipe cycle, said motor including two terminals, first means for connecting a first one of said two terminals to a source of a first potential, and second means for connecting the second one of said two terminals to a source of a second potential, said second connecting means including two parallel paths, a first of said paths including a motor park switch and the second of said paths including a bimetal element and a heater resistance element therefor, said bimetal element having normally open contacts and operative to close following a dwell period after each wipe cycle, the opening of said normally open contacts being dependent on the cooling rate of said bimetal element.
 2. An intermittent control for a windshield wiper system in accordance with claim 1 further including manually adjustable means for varying the closure time of said bimetal element.
 3. An intermittent control for a windshield wIper system in accordance with claim 2 further including an additional resistance element connected in series with said motor terminals, and a thermistor heat-coupled to said additional resistance element and connected in series with said resistance element.
 4. An intermittent control for a windshield wiper system in accordance with claim 3 wherein said manually adjustable means is a variable resistance connected in series with said heater resistance element.
 5. An intermittent control for a windshield wiper system in accordance with claim 3 further including an additional thermistor heat-coupled to said additional resistance and element connected in series with said motor terminals for controlling the speed of said motor in accordance with the temperature of said additional resistance element.
 6. An intermittent control for a windshield wiper system in accordance with claim 2 wherein said manually adjustable means is a variable resistance connected in series with said heater resistance element.
 7. An intermittent control for a windshield wiper system in accordance with claim 3 further including an additional resistance element connected in series with said motor terminals, and a thermistor heat-coupled to said additional resistance element and connected in series with said heater resistance element.
 8. An intermittent control for a windshield wiper system in accordance with claim 7 wherein said motor park switch is operative to connect said second motor terminal to said source of said second potential when said motor is out of its park position and further including a brake resistance, said motor park switch being further operative to connect said brake resistance across said switch terminals when said motor is in its park position.
 9. An intermittent control for a windshield wiper system in accordance with claim 1 further including switch means having three positions, a first of said positions for deenergizing said motor, the second of said positions for connecting said second motor terminal to said source of said second potential bypassing said second connecting means, and the third of said positions for enabling the operation of said second path connecting means.
 10. An intermittent control for a windshield wiper system in accordance with claim 9 further including means operative when said switch means is moved from said first position to said third position for momentarily providing an alternate path from said second motor terminal to said source of said second potential.
 11. An intermittent control for a windshield wiper system in accordance with claim 1 further including switch means having three positions, a first of said positions for deenergizing said motor, the second of said positions for connecting said second motor terminal to said source of said second potential bypassing said second connecting means, and the third of said positions for enabling the operation of said second path connecting means.
 12. An intermittent control for a windshield wiper system in accordance with claim 11 further including means operative when said switch means is moved from said first position to said third position for momentarily providing an alternate path from said second motor terminal to said source of said second potential. 